Actually there is abrasion and/or chemical cleaning. SS falls on the abrasion side. If you add Lemishine, and Dawn in the water, add chemical to that. When you think about it, even rouge polishes because of microscopic "rocks", that eat and smooth brass. The process of polishing is just making the scratches tinier. So if you Really, Really, want it polished with a tumber, run it 2 hours in a wet Thumlers, dry it, then tumble for 24 hours in rouge charged corncob. Yeah okay a little radical. Ever watch a rock polishing machine.....geeze those guys that do that are patient. Weeks....

Now one more factor. There is a kinda, somewhat, just a little truth, to the argument that tumbling pockets clean, chemical or SS abrasion makes primers go in harder (can you say, "more friction"). It would seem that the primer residue has bit of a lubrication property. Same thing with neck interiors and powder residue.

If that affects your seating methods negatively, just tumble for 5 minutes in pure corncob. You know that fine white stuff that's left? That has lube properties too. That means both bullets and primers go in easier.